The bug actually appeared because the Bravais matrix was not read in
correctly. The scaling was applied in a wrong way.
The bug affected the size of the MT radii. Therefore I first assumed
that it was related to global/chkmt.f90. It was not. In fact, I wrote
super code in global/chkmt.f90. :)

The parameter maxCubeAtoms is used in chkmt to determine the
size of some arrays. It was chosen too small for some limiting
cases.
Also in this commit: Added an error message for too small distances
between atoms.

This commit introduces the new chkmt.f90. Besides some exceptions this
new routine should yield the same results as the old one. With a runtime
scaling of O(N_atoms) it overcomes the bad O(N_atoms^4) scaling of the
old pendant.